1. Field of the Invention
The present invention relates to an electronic blackboard for processing image information which corresponds to the image or the like displayed on the writing surface and its accessories such as writing tools.
2. Prior Art
Hitherto, there is a conventional electronic blackboard apparatus (called "an electromagnetic coupled type" hereinafter) arranged such that a multiplicity of sensing lines are, in both x and y directions, formed on the reverse side of the writing surface thereof and a writing tool comprising a felt pen or the like is provided with a coil as to generate flux change when an electronic current is passed so that the thus-generated flux change is detected by the sensing lines or the other end of the coil so that the position of the writing tool on the writing surface is detected and thereby image information which corresponds to the image displayed on the writing surface can be processed.
Another type of the electronic blackboard apparatus called "a photoelectric transfer type" hereinafter) is known which is arranged such that an image written on a whiteboard or a flexible seat with a writing tool such as a felt pen or the like is scanned by a scanner which can move along the surface of this whiteboard or by a stationary scanner with this seat wound up as to be photoelectrically transferred to image information.
The other conventional electronic blackboard apparatus (called "a pressure sensing type" hereinafter) is known in which two resistance plates provided with electrodes on the opposing sides thereof are fastened to the reverse side of a writing surface made of a flexible material. The various parts are laminated to each other. These two resistance plates are fastened to the electrodes in such a manner that these electrodes are positioned in the vertical or lateral direction. Therefore, a displacement current is generated between an electrode on one resistance plate and the electrode on the other resistance plate when the writing tool is moved along the surface of the writing surface with an electric current being passed through either of the two resistance plates. On the basis of the thus-generated displacement current, the position of the writing tool on the writing surface is detected so that image information corresponding to the image displayed on the writing surface is processed.
However, the above-described electromagnetic coupling type apparatus has a problem in that, a cord needs to be provided between the control unit for detecting position and a coil provided for the writing tool. The thus-provided cord readily deteriorates in handling the writing tool.
In the photoelectrically transfer type apparatus, the writing tool can be arranged to be a cord-less type. However, another problem arises in that information corresponding to the displayed image cannot be obtained during writing of the image on the writing surface, that is a real-time image cannot be obtained since image information can be first obtained when the scanner is moved or the seat is wound up.
In the pressure sensing type apparatus, the writing tool can be arranged to be a cord-less type and the information corresponding to the image which is being written can be obtained. However, a problem arises in that the thickness and the weight become excessive since the structure needs to be formed to withstand the pressure applied with the writing tool to the writing surface.